A plasma catalyst, its preparation method and application

Abstract

The present invention relates to the field of plasma catalysts, and discloses a plasma catalyst, a preparation method thereof, and an application thereof. The catalyst contains a carrier, and an active component element and a promoter element supported on the carrier. The carrier is selected from at least one of Al 2 O 3 , SiO 2 , MgO, ZrO 2 , and molecular sieve. The active component element is selected from at least one of Pt, Rh, Pd, and Ir. The promoter element is selected from at least one of Group VIII non-noble metal elements and Group IB metal elements. The catalyst provided by the present invention can adapt to the composition change of the tail gas after the plasma reaction of natural gas, realize the one-step conversion of natural gas into acrylic acid under low temperature and normal pressure, and can effectively and stably improve the selectivity of acrylic acid.

Description

Technical Field

[0001] The present invention relates to the field of plasma catalysts, and specifically, to a plasma catalyst, a preparation method thereof, and an application thereof. Background Art

[0002] The development of oil and gas has driven the rapid development of fine chemicals. As one of the important fine chemical raw materials, acrylic acid is widely used in fields such as coatings, building materials, adhesives, textiles, leather, papermaking, oil extraction, and water treatment.

[0003] The main synthesis methods of acrylic acid include chloroethanol method, cyanoethanol method, high-pressure Reppe and modified Reppe methods, formaldehyde-acetic acid method, acrylonitrile hydrolysis method, ethylene method, propylene direct oxidation method, propane oxidation method, and ethylene oxide method, etc. Among them, the only method for large-scale industrial production of acrylic acid is the two-step oxidation method using propylene as the raw material. The main raw material propylene is obtained from petroleum cracking. With the increasing shortage of petroleum resources, the synthesis cost of acrylic acid has increased significantly.

[0004] In recent years, in addition to improving the propylene oxidation process, certain progress has also been made in the research and development of other methods for synthesizing acrylic acid in China. The acetylene hydroxylation method for synthesizing acrylic acid by the non-petroleum route does not rely on petroleum and is suitable for oil-poor, gas-rich, or coal-rich countries and regions. China is oil-poor and coal-rich, with a huge production capacity of calcium carbide from coal, and a large amount of CO in the tail gas of calcium carbide method for producing acetylene can be used as a raw material for synthesizing acrylic acid by acetylene hydroxylation. However, coal chemical industry has a large water consumption and high energy consumption in the coal gasification stage, and most coal-rich areas are short of water, which severely restricts the development of acrylic acid production by acetylene method.

[0005] Currently, with the development of combustible ice and shale gas, the natural gas reserves are sufficient, and the natural gas conversion and utilization technology has become a hot topic. The process of converting natural gas into acrylic acid has become a new direction for technological development. Plasma converts natural gas, and under the action of an electric field, methane is activated by electron collision, and then free radicals collide and couple to form products. The plasma method has the characteristics of simple operation, small device volume, high energy density, and short reaction time, and can realize the conversion of natural gas at a lower temperature, which is suitable for occasions with different scales, scattered layouts, and variable production conditions. The conversion of methane by plasma technology can be carried out at normal temperature and pressure, the operating conditions are relatively mild, the selectivity of specific products is high, and the main product is acetylene.

[0006] Therefore, it is necessary to provide a post-treatment catalyst suitable for direct plasma conversion of natural gas. Summary of the Invention

[0007] The purpose of the present invention is to overcome the defect that the selectivity of acrylic acid in the conversion of methane to olefins in the prior art is not high.

[0008] To achieve the above object, a first aspect of the present invention provides a plasma catalyst, which contains a carrier and active component elements and promoter elements supported on the carrier. The carrier is selected from at least one of Al 2 O 3 , SiO 2 , MgO, ZrO 2 , and molecular sieves. The active component elements are selected from at least one of Pt, Rh, Pd, and Ir. The promoter elements are selected from at least one of Group VIII non-noble metal elements and Group IB metal elements;

[0009] Based on the total weight of the catalyst, the content of the active component elements by element is 0.01-0.1% by weight, and the content of the promoter elements by element is 0.1-2% by weight.

[0010] The inventors of the present invention found that the addition of promoter elements can change the loading state of the active component metal elements on the catalyst carrier, improve the dispersion degree on the surface of the loaded metal, increase the electrons on the metal surface, and at the same time improve the bimetallic contact surface. And the electron-rich state can weaken the adsorption of the active component metal elements on carbon atoms, strengthen the adsorption of oxygen atoms, which is beneficial to the carbonylation of acetylene and CO, thereby improving the selectivity of acrylic acid. The improvement of the acrylic acid selectivity is beneficial to reducing the unit consumption of the product, and further can improve the economy of the methane conversion process. In view of this, the solution of the present invention is provided.

[0011] A second aspect of the present invention provides a preparation method for the plasma catalyst described in the first aspect above. The method includes: impregnating the pretreated carrier in an aqueous solution containing an active component element source and a promoter element source, and then successively performing drying treatment and calcination treatment on the solid obtained after impregnation.

[0012] A third aspect of the present invention provides the application of the plasma catalyst described in the first aspect above in the post-treatment of direct conversion of natural gas.

[0013] The catalyst provided by the present invention has the advantages of low loading, low cost, safety and environmental protection. And the catalyst is heated by the heat generated after the plasma conversion of methane, without the need for an additional heat source to activate the catalyst, can adapt to the composition change of the tail gas caused by the unstable discharge in the plasma process, realizes the one-step conversion of acrylic acid under low temperature and normal pressure, and can effectively and stably improve the selectivity of acrylic acid. Detailed Embodiments

[0014] The endpoints and any values disclosed in this text for ranges are not limited to the exact ranges or values. These ranges or values should be understood to include values close to these ranges or values. For numerical ranges, between the endpoint values of each range, between the endpoint values of each range and individual point values, and between individual point values, they can be combined with each other to obtain one or more new numerical ranges, and these numerical ranges should be regarded as specifically disclosed in this text.

[0015] As described above, the first aspect of the present invention provides a plasma catalyst, which contains a carrier and active component elements and promoter elements supported on the carrier. The carrier is selected from at least one of Al 2 O 3 , SiO 2 , MgO, ZrO 2 , molecular sieves. The active component elements are selected from at least one of Pt, Rh, Pd, and Ir. The promoter elements are selected from at least one of Group VIII non-noble metal elements and Group IB metal elements;

[0016] Based on the total weight of the catalyst, the content of the active component elements by element is 0.01 - 0.1% by weight, and the content of the promoter elements by element is 0.1 - 2% by weight.

[0017] Preferably, the carrier is selected from at least one of Al 2 O 3 , SiO 2 , MgO.

[0018] Preferably, the average particle size of the carrier is 3 - 5 mm, preferably 3 - 3.5 mm.

[0019] Preferably, based on the total weight of the catalyst, the content of the active component elements by element is 0.05 - 0.1% by weight, and the content of the promoter elements by element is 0.1 - 1% by weight. The inventors of the present invention found that the catalyst in this preferred case has higher acrylic acid selectivity.

[0020] Preferably, the promoter elements are selected from at least one of Ni, Fe, Cu, Ag, and Au.

[0021] As described above, the second aspect of the present invention provides a method for preparing the plasma catalyst described in the first aspect above. The method includes: impregnating the pretreated carrier in an aqueous solution containing a source of active component elements and a source of promoter elements, and then successively drying and calcining the obtained solid.

[0022] According to a preferred specific embodiment of the present invention, the steps of the pretreatment include:

[0023] The carrier to be pre-treated is successively subjected to first drying and first calcination to obtain intermediate I;

[0024] Then, the intermediate I is subjected to a contact reaction with a solvent, and the solid obtained after the contact of the mixture after the contact reaction with titanium tetrachloride is successively subjected to second drying and second calcination.

[0025] Preferably, the contact reaction is carried out under ultrasonic conditions, and the conditions of the ultrasonic wave at least satisfy: the ultrasonic time is 1 - 3 h, and the ultrasonic frequency is 10 KHz - 40 KHz. More preferably, the conditions of the ultrasonic wave at least satisfy: the ultrasonic time is 1.5 - 2 h, and the ultrasonic frequency is 20 KHz - 25 KHz.

[0026] Preferably, the conditions of the first drying at least satisfy: the drying time is 8 - 12 h, and the drying temperature is 100 - 120 °C.

[0027] Preferably, the conditions of the first calcination at least satisfy: the calcination time is 2 - 6 h, the calcination temperature is 450 - 500 °C, and the heating rate is 1 - 4 °C / min.

[0028] It should be noted that the heating rate represents the amount of temperature change per unit time. The timing point of the calcination is when the temperature rises to the set calcination temperature value. The present invention has no particular limitation on the way of heating, and those skilled in the art can select it in combination with the known technologies in the art. An exemplary heating method is provided in the following text of the present invention, and those skilled in the art should not understand it as a limitation to the present invention.

[0029] Preferably, the solvent is selected from at least one of absolute ethanol, methanol, and glycerol.

[0030] Preferably, the dosage ratio of the intermediate I to the solvent is 1 g: 10 - 100 mL.

[0031] Preferably, the weight ratio of the dosage of the intermediate I to the titanium tetrachloride is 1: 1 - 10.

[0032] According to another preferred specific embodiment of the present invention, the conditions of the second drying at least satisfy: the drying time is 10 - 15 h, and the drying temperature is 100 - 120 °C. Preferably, the conditions of the second drying at least satisfy: the drying time is 11 - 12 h, and the drying temperature is 100 - 120 °C.

[0033] Preferably, the conditions of the second calcination at least satisfy: the calcination time is 4 - 8 h, the calcination temperature is 450 - 500 °C, and the heating rate is 1 - 4 °C / min.

[0034] Preferably, the active component element source is selected from at least one of nitrates, acetates, and chlorides that can provide the active component elements. Exemplarily, the active component element source can be rhodium nitrate, iridium acetate, chloroplatinic acid, and palladium acetate.

[0035] Preferably, the promoter element source is selected from at least one of nitrates and chlorides that can provide the promoter elements. Exemplarily, the promoter element source can be iron nitrate, copper nitrate, silver nitrate, and chloroauric acid.

[0036] Preferably, the impregnation conditions satisfy at least: the impregnation time is 8 - 12 h, and the impregnation temperature is 20 - 30 °C.

[0037] Preferably, the drying conditions satisfy at least: the drying time is 11 - 12 h, and the drying temperature is 100 - 120 °C.

[0038] Preferably, the calcination conditions satisfy at least: the calcination time is 6 - 12 h, the calcination temperature is 450 - 500 °C, and the heating rate is 1 - 4 °C / min.

[0039] As described above, the third aspect of the present invention provides the application of the plasma catalyst described in the first aspect in the post-treatment of direct conversion of natural gas.

[0040] The present invention will be described in detail below by examples. In the following examples, unless otherwise specified, all raw materials are commercially available products, the element content is measured by ICP, and the average particle size is measured by a particle size analyzer.

[0041] Support:

[0042] Al 2 O 3 : Purchased from Aladdin Reagent Co., Ltd., with an average particle size of 3.5 mm.

[0043] SiO 2 : Purchased from Aladdin Reagent Co., Ltd., with an average particle size of 3.5 mm.

[0044] MgO: Purchased from Aladdin Reagent Co., Ltd., with an average particle size of 3.5 mm.

[0045] Active component element source:

[0046] Iron nitrate: Analytically pure, purchased from Aladdin Reagent Co., Ltd.

[0047] Copper nitrate: Analytically pure, purchased from Aladdin Reagent Co., Ltd.

[0048] Silver nitrate: Analytically pure, purchased from Aladdin Reagent Co., Ltd.

[0049] Promoter element source:

[0050] Rhodium nitrate: analytically pure, purchased from Aladdin Reagent Company.

[0051] Iridium acetate: analytically pure, purchased from Aladdin Reagent Company.

[0052] Chloroplatinic acid: analytically pure, purchased from Aladdin Reagent Company.

[0053] Plasma reactor: Refer to patent document CN109289457A. Specifically, the plasma reactor includes a blade sliding arc stabilization system and a reactor:

[0054] The blade sliding arc stabilization system includes a first DC power supply, a second DC power supply, an inductance coil, a diode, and an electromagnetic relay switch. The first DC power supply is connected in series with the inductance coil and the diode, and the electromagnetic relay switch and the second DC power supply are connected in series. The two series branches are connected in parallel and then connected to the two electrodes of the reactor. The positive and negative poles of the two DC power supplies are in the same direction and the negative pole is grounded: The first DC power supply uses a 1.5 kV DC power supply, the second DC power supply uses a 10 kV DC power supply, and the inductance coil 6 uses a 30 mH inductance coil; The breakdown voltage is provided by the second DC power supply, and the power supply is maintained by the first DC power supply;

[0055] The reactor includes an outer cover, two electrodes, two flat magnets, and a nozzle; The electrodes are arc-shaped blade electrodes (radius 20 mm), both arranged on the lower wall plate of the reactor and placed opposite to each other; The outer cover is a straight quadrangular prism structure, with a rectangular cross-section (made of quartz, 45 mm * 12 mm * 110 mm, wall thickness 2 mm), and two flat magnets are arranged parallel to each other outside the outer cover; The nozzle (diameter 2 mm) is arranged on the lower wall plate of the reactor corresponding to the middle of the two electrodes to spray gas into the reactor interior, and the distance from the nozzle outlet to the narrowest part of the two electrodes is 10 mm; The upper and lower wall plates of the reactor are made of high-temperature resistant insulating material alumina ceramic, and graphite gaskets are padded between the upper and lower wall plates and the outer cover, and the upper and lower wall plates are fixed by screws and nuts to fix the outer cover.

[0056] Preparation Example 1: Preparation of carrier Z1

[0057] Put Al 2 O 3 The carrier is dried in an oven at 120 °C (i.e., the first drying) for 12 h and then placed in a muffle furnace, and is calcined (i.e., the first calcination) at a heating rate of 3 °C / min to 450 °C for 4 h to obtain intermediate I;

[0058] Add 40 g of the intermediate I to 400 mL of absolute ethanol and ultrasonicate for 2 h at an ultrasonic frequency of 25 KHz; after ultrasonication, add 40 g of titanium tetrachloride dropwise, then perform rotary evaporation. After obtaining a solid, place it in an oven at 120 °C for drying (i.e., the second drying) for 12 h, and then place it in a muffle furnace. Raise the temperature to 450 °C at a heating rate of 3 °C / min and calcine (i.e., the second calcination) for 5 h to obtain the pretreated support Z1;

[0059] Preparation Example 2: Preparation of support Z2

[0060] Place the Al 2 O 3 support in an oven at 100 °C for drying (i.e., the first drying) for 10 h, and then place it in a muffle furnace. Raise the temperature to 500 °C at a heating rate of 4 °C / min and calcine (i.e., the first calcination) for 3 h to obtain the intermediate I;

[0061] Add 40 g of the intermediate I to 800 mL of absolute ethanol and ultrasonicate for 2 h at an ultrasonic frequency of 20 KHz; after ultrasonication, add 90 g of titanium tetrachloride dropwise, then perform rotary evaporation. After obtaining a solid, place it in an oven at 100 °C for drying (i.e., the second drying) for 10 h, and then place it in a muffle furnace. Raise the temperature to 500 °C at a heating rate of 4 °C / min and calcine (i.e., the second calcination) for 5 h to obtain the pretreated support Z2.

[0062] Preparation Example 3: Preparation of catalyst C1

[0063] Place 40 g of the support Z1 prepared in Preparation Example 1 in a mixed solution for impregnation for 12 h. The mixed solution contains 1.2 g of rhodium nitrate solution (rhodium content is 5 wt%), 0.7 g of iron nitrate solution (iron content is 30 wt%), and 100 mL of deionized water. Then, perform rotary evaporation in a water bath at 80 °C for 4 h and place it in an oven for drying at 120 °C for 8 h. Subsequently, place it in a muffle furnace. Raise the temperature to 450 °C at a heating rate of 3 °C / min and calcine for 5 h to obtain the catalyst, denoted as C1.

[0064] Among them, the content of the active component element rhodium in the catalyst C1 is 0.1 wt%, and the content of the promoter element iron is 1 wt%.

[0065] Preparation Example 4: Preparation of catalyst C2

[0066] This preparation example adopts a preparation method similar to that of Preparation Example 3. The difference is that:

[0067] Replace the rhodium nitrate solution with an iridium acetate solution with an active component element mass concentration of 10 wt% in an equal volume manner to obtain the catalyst, denoted as C2.

[0068] Among them, the content of the active component element iridium in the catalyst C2 is 0.08 wt%, and the content of the promoter element iron is 1 wt%.

[0069] Preparation Example 5: Preparation of Catalyst C3

[0070] This preparation example uses a preparation method similar to that of Preparation Example 3, the difference being that:

[0071] The rhodium nitrate solution is replaced with an equal volume of chloroplatinic acid solution with an active component element mass concentration of 12 wt%, and the obtained catalyst is denoted as C3.

[0072] Among them, the content of the active component element platinum in catalyst C3 is 0.09 wt%, and the content of the promoter element iron is 1 wt%.

[0073] Preparation Example 6: Preparation of Catalyst C4

[0074] This preparation example uses a preparation method similar to that of Preparation Example 3, the difference being that:

[0075] The carrier Z1 is replaced with an equal weight of carrier Z2, and the iron nitrate solution is replaced with an equal volume of copper nitrate solution with the same mass concentration of the promoter element, and the obtained catalyst is denoted as C4.

[0076] Among them, the content of the active component element rhodium in catalyst C4 is 0.1 wt%, and the content of the promoter element copper is 1.5 wt%.

[0077] Preparation Example 7: Preparation of Catalyst C5

[0078] This preparation example uses a preparation method similar to that of Preparation Example 3, the difference being that:

[0079] The iron nitrate solution is replaced with an equal volume of silver nitrate solution with the same mass concentration of the promoter element, and the obtained catalyst is denoted as C5.

[0080] Among them, the content of the active component element rhodium in catalyst C5 is 0.1 wt%, and the silver content of the promoter element is 0.8 wt%.

[0081] Preparation Example 8: Preparation of Catalyst C6

[0082] This preparation example uses a preparation method similar to that of Preparation Example 3, the difference being that:

[0083] Replace the Al 2 O 3 carrier with an equal weight of SiO 2 carrier to obtain a catalyst denoted as C6.

[0084] Among them, the content of the active component element rhodium in catalyst C6 is 0.1 wt%, and the content of the promoter element iron is 1 wt%.

[0085] Preparation Example 9: Preparation of Catalyst C7

[0086] This preparation example uses a preparation method similar to that of Preparation Example 3, except that:

[0087] Replace the Al 2 O 3 support with an equal weight of MgO support to obtain a catalyst, denoted as C7.

[0088] Among them, the content of the active component element rhodium in catalyst C7 is 0.1% by weight, and the content of the promoter element iron is 1% by weight.

[0089] Preparation Example 10: Preparation of catalyst C8

[0090] This preparation example uses a preparation method similar to that of Preparation Example 3, except that:

[0091] First, impregnate the support Z1 in a rhodium nitrate solution and then perform drying treatment and calcination treatment in sequence to obtain support Z11;

[0092] Then, impregnate the support Z11 in an iron nitrate solution and then perform drying treatment and calcination treatment in sequence to obtain a catalyst, denoted as C8.

[0093] Among them, the content of the active component element rhodium in catalyst C8 is 0.1% by weight, and the content of the promoter element iron is 1% by weight.

[0094] Preparation Example 11: Preparation of catalyst C9

[0095] This preparation example uses a preparation method similar to that of Preparation Example 3, except that:

[0096] First, impregnate the support Z1 in an iron nitrate solution and then perform drying treatment and calcination treatment in sequence to obtain support Z12;

[0097] Then, impregnate the support Z12 in a rhodium nitrate solution and then perform drying treatment and calcination treatment in sequence to obtain a catalyst, denoted as C9.

[0098] Among them, the content of the active component element rhodium in catalyst C9 is 0.1% by weight, and the content of the promoter element iron is 1% by weight.

[0099] Comparative Example 1: Preparation of catalyst DC1

[0100] This comparative example uses a preparation method similar to that of Preparation Example 3, except that:

[0101] Replace the support Z1 with an equal weight of support Z2, and replace the rhodium nitrate solution with an equal volume of iron nitrate solution with the same mass concentration of the active component element to obtain a catalyst, denoted as DC1.

[0102] Among them, the content of the promoter element iron in the catalyst DC1 is 1% by weight.

[0103] Comparative Example 2: Preparation of catalyst DC2

[0104] This comparative example uses a preparation method similar to that of Preparation Example 3, except that:

[0105] The iron nitrate solution is replaced with an equal volume of a rhodium nitrate solution having the same mass concentration of the active component element to obtain a catalyst, denoted as DC2.

[0106] Among them, the content of the active component element rhodium in the catalyst DC2 is 0.1% by weight.

[0107] Comparative Example 3: Preparation of catalyst DC3

[0108] This comparative example uses a preparation method similar to that of Preparation Example 3, except that:

[0109] The support Z1 is replaced with an equal weight of support Z2, and the rhodium nitrate solution is replaced with an equal volume of an iron nitrate solution having the same mass concentration of the promoter element to obtain a catalyst, denoted as DC3.

[0110] Among them, the content of the promoter element iron in the catalyst DC3 is 1.1% by weight.

[0111] Comparative Example 4: Preparation of catalyst DC4

[0112] This comparative example uses a preparation method similar to that of Preparation Example 3, except that:

[0113] The iron nitrate solution is replaced with an equal volume of a rhodium nitrate solution having the same mass concentration of the active component element to obtain a catalyst, denoted as DC4.

[0114] Among them, the content of the active component element rhodium in the catalyst DC4 is 1.1% by weight.

[0115] Comparative Example 5: Preparation of catalyst DC5

[0116] This comparative example uses a preparation method similar to that of Preparation Example 4, except that:

[0117] The iron nitrate solution is replaced with an equal volume of an iridium acetate solution having the same mass concentration of the active component element to obtain a catalyst, denoted as DC5.

[0118] Among them, the content of the active component element iridium in the catalyst DC5 is 1.1% by weight.

[0119] Comparative Example 6: Preparation of catalyst DC6

[0120] This comparative example uses a preparation method similar to that of Preparation Example 5, except that:

[0121] The iron nitrate solution was replaced with an equal volume of chloroplatinic acid solution having the same mass concentration of the active component element to obtain a catalyst, denoted as DC6.

[0122] Among them, the content of the active component element platinum in the catalyst DC6 is 1.1% by weight.

[0123] Test Example

[0124] The catalyst (40 g) prepared in the above example was placed in a plasma reactor for reaction. Among them, the methane flow rate was 0.5 L / min, the hydrogen flow rate was 1.5 L / min, the carbon monoxide flow rate was 1.5 L / min, the discharge power was 110 W, and the reaction was stably carried out under continuous discharge for 1 h. The methane conversion rate, acetylene selectivity, and acrylic acid selectivity were calculated. The corresponding process conditions and results are shown in Table 1.

[0125] The methane conversion rate is expressed as: methane conversion rate = (methane inlet molar amount - methane outlet molar amount) / methane inlet molar amount × 100%;

[0126] The acetylene selectivity is expressed as: (acetylene outlet molar amount) × 2 / (methane inlet molar amount - methane outlet molar amount) × 100%;

[0127] The acrylic acid selectivity is expressed as: (acrylic acid outlet molar amount) × 3 / (methane inlet molar amount - methane outlet molar amount) × 100%.

[0128] (The inlet molar amount or outlet molar amount means the molar amount of the gas taken for one minute at the inlet or outlet after the reaction reaches equilibrium.)

[0129] Table 1

[0130]

[0131] Table 1 (continued)

[0132] Preparation Example 9 Comparative Example 1 Comparative Example 2 Comparative Example 3 Comparative Example 4 Comparative Example 5 Comparative Example 6 Catalyst type C9 DC1 DC2 DC3 DC4 DC5 DC6 Temperature, °C 42 46 49 48 51 46 44 Pressure, MPa 0.14 0.15 0.16 0.15 0.14 0.13 0.16 Methane conversion rate, % 36 33 35 37 34 35 36 Acetylene selectivity, % 15 12 9 5 21 16 19 Acrylic acid selectivity, % 76 30 45 35 46 56 49

[0133] It can be seen from the results in Table 1 that the catalyst provided by the present invention can adapt to the composition change of the tail gas after the plasma reaction of natural gas, realize the one-step conversion of natural gas to acrylic acid under low temperature and normal pressure, and can effectively and stably improve the selectivity of acrylic acid.

[0134] The preferred embodiments of the present invention have been described in detail above. However, the present invention is not limited thereto. Within the scope of the technical concept of the present invention, various simple modifications can be made to the technical solutions of the present invention, including any other suitable combination of each technical feature. These simple modifications and combinations should also be regarded as the content disclosed by the present invention and fall within the protection scope of the present invention.

Claims

1. A method for preparing a plasma catalyst, characterized in that, the method comprises: impregnating a pretreated carrier in an aqueous solution containing an active component element source and a promoter element source, and then successively drying and calcining the obtained solid after impregnation; wherein, the steps of the pretreatment include: successively drying and calcining the carrier to be pretreated to obtain intermediate I; then, contacting intermediate I with a solvent for a reaction, and successively drying and calcining the solid obtained after contacting the mixture after the contacting reaction with titanium tetrachloride; the contacting reaction is carried out under ultrasonic conditions; The plasma catalyst contains a carrier, and an active component element and a promoter element supported on the carrier. The carrier is selected from at least one of Al 2 O 3 , SiO 2 , MgO, ZrO 2 , and molecular sieve. The active component element is selected from at least one of Pt, Rh, Pd, and Ir. The promoter element is selected from at least one of Group VIII non-noble metal elements and Group IB metal elements; based on the total weight of the catalyst, the content of the active component element by element is 0.01-0.1% by weight, and the content of the promoter element by element is 0.1-2% by weight.

2. The method according to claim 1, wherein, The carrier is selected from at least one of Al 2 O 3 , SiO 2 , and MgO.

3. The method according to claim 1 or 2, wherein, the average particle size of the carrier is 3-5 mm.

4. The method according to claim 1 or 2, wherein, based on the total weight of the catalyst, the content of the active component element by element is 0.05-0.1% by weight, and the content of the promoter element by element is 0.1-1% by weight.

5. The method according to claim 1 or 2, wherein, the promoter element is selected from at least one of Ni, Fe, Cu, Ag, and Au.

6. The method according to claim 1 or 2, wherein, the conditions of the ultrasonic at least satisfy: the ultrasonic time is 1-3 h, and the ultrasonic frequency is 10 KHz-40 KHz.

7. The method according to claim 1 or 2, wherein, the conditions of the first drying at least satisfy: the drying time is 8-12 h, and the drying temperature is 100-120 °C.

8. The method according to claim 1 or 2, wherein, the conditions of the first calcination at least satisfy: the calcination time is 2-6 h, the calcination temperature is 450-500 °C, and the heating rate is 1-4 °C / min.

9. The method according to claim 1 or 2, wherein, the solvent is selected from at least one of anhydrous ethanol, methanol, and glycerol.

10. The method according to claim 1 or 2, wherein, the dosage ratio of intermediate I to the solvent is 1 g: 10-100 mL.

11. The method according to claim 1 or 2, wherein, the weight ratio of intermediate I to titanium tetrachloride is 1: 1-10.

12. The method according to claim 1 or 2, wherein, the conditions of the second drying at least satisfy: the drying time is 10-15 h, and the drying temperature is 100-120 °C.

13. The method according to claim 1 or 2, wherein, the conditions of the second calcination at least satisfy: the calcination time is 4-8 h, the calcination temperature is 450-500 °C, and the heating rate is 1-4 °C / min.

14. The method according to claim 1 or 2, wherein, the active component element source is selected from at least one of nitrates, acetates, and chlorides that can provide the active component element.

15. The method according to claim 1 or 2, wherein, the promoter element source is selected from at least one of nitrates and chlorides capable of providing the promoter element.

16. The method according to claim 1 or 2, wherein, the conditions of the impregnation satisfy at least: the impregnation time is 8 - 12 h, and the impregnation temperature is 20 - 30 °C.

17. The method according to claim 1 or 2, wherein, the conditions of the drying satisfy at least: the drying time is 11 - 12 h, and the drying temperature is 100 - 120 °C.

18. The method according to claim 1 or 2, wherein, the conditions of the calcination satisfy at least: the calcination time is 6 - 12 h, the calcination temperature is 450 - 500 °C, and the heating rate is 1 - 4 °C / min.

19. Application of the plasma catalyst prepared by the method according to any one of claims 1 - 18 in the post - treatment of direct conversion of natural gas.

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